They're here! After wandering in the Martian desert for 25 months, NASA's Curiosity rover has finally arrived at its promised land: the base of Mt. Sharp, the 3-mile-high mound in in the middle of Gale Crater.
The arrival marks the beginning of the Mars Science Laboratory rover's original mission: to read the mountain's clay-rich lower layers like pages in a history book, pages that could reveal an array of life-friendly environments on the Red Planet.
"We have finally arrived at the far frontier that we have sought for so long," said project scientist and Caltech geologist John Grotzinger.
Getting to Mt. Sharp has been a long time coming. The trip was delayed in part by a detour the rover took to look at a promising spot called Yellowknife Bay. Though it cost the team at Jet Propulsion Laboratory about half a year, the gamble paid off; rocks drilled there revealed a smorgasbord of chemical elements that would have been suitable for microbial life, if it ever existed.
Now that the scientists know habitable environments did exist on the Red Planet, part of the next step will be looking for those particular environments that have a higher likelihood of preserving organic molecules, Grotzinger said.
The rover is closing in on a spot known as Pahrump Hills, an outcrop that wasn't on the original itinerary – a happy outcome of the detour Curiosity took to avoid sharp rocks that had been causing an alarming amount of damage on the rover's thin wheels. This spot will now be the gateway to Mt. Sharp, and it probably holds Curiosity's first official drilling target. Grotzinger said the rover would make it there in the next week or two.
The scientists are particularly interested in a stretch of rock known as the Murray Formation, which it will cross en route to its original stopping point, Murray Buttes. Kathryn Stack, Curiosity rover mission scientist, pointed out that the Murray Formation could provide an unprecedented wealth of information about the history of habitable environments on Mars. After all, the Yellowknife Bay formation where Curiosity found its first life-friendly spot was only 5 meters thick, representing perhaps thousands to hundreds of thousands of years of sedimentary deposits. The Murray Formation, by contrast, is 200 meters thick.
"We potentially have millions to tens of millions of years of Martian history just waiting for us to explore," Stack said.
The hard part, scientists said, will be deciding how much time to devote to Pahrump Hills, Murray Buttes and the next interesting unit up the slopes, called Hematite Ridge. Grotzinger said he was particularly interested in the silicon in the upcoming rocks, because the element's distribution can often signal the movement of water.
Mission officials also responded to criticsm from a NASA Planetary Senior Review panel report released this summer. The report contended that the plan to explore Mt. Sharp did not make good use of the rover's instruments, calling it "a poor science return for such a large investment in a flagship mission."
"I think the principal recommendation of the panel is that we drive less and drill more," Grotzinger said, and he said that's not far from what they are going to end up doing. "I think that the recommendations of the review and what we want to do as a science team are going to align, because we have now arrived at Mt. Sharp, we are going to do a lot more drilling."